Date:   Tue, 10 Jan 2023 02:33:18 -0600
From:   "Kalra, Ashish" <ashish.kalra@....com>
To:     Alexey Kardashevskiy <aik@....com>,
        Michael Roth <michael.roth@....com>, kvm@...r.kernel.org
Cc:     linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        luto@...nel.org, dave.hansen@...ux.intel.com, slp@...hat.com,
        pgonda@...gle.com, peterz@...radead.org,
        srinivas.pandruvada@...ux.intel.com, rientjes@...gle.com,
        dovmurik@...ux.ibm.com, tobin@....com, bp@...en8.de,
        vbabka@...e.cz, kirill@...temov.name, ak@...ux.intel.com,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
        dgilbert@...hat.com, jarkko@...nel.org, harald@...fian.com,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH RFC v7 52/64] KVM: SVM: Provide support for
 SNP_GUEST_REQUEST NAE event


On 1/9/2023 8:28 PM, Alexey Kardashevskiy wrote:
> 
> 
> On 10/1/23 10:41, Kalra, Ashish wrote:
>> On 1/8/2023 9:33 PM, Alexey Kardashevskiy wrote:
>>> On 15/12/22 06:40, Michael Roth wrote:
>>>> From: Brijesh Singh <brijesh.singh@....com>
>>>>
>>>> Version 2 of GHCB specification added the support for two SNP Guest
>>>> Request Message NAE events. The events allows for an SEV-SNP guest to
>>>> make request to the SEV-SNP firmware through hypervisor using the
>>>> SNP_GUEST_REQUEST API define in the SEV-SNP firmware specification.
>>>>
>>>> The SNP_EXT_GUEST_REQUEST is similar to SNP_GUEST_REQUEST with the
>>>> difference of an additional certificate blob that can be passed through
>>>> the SNP_SET_CONFIG ioctl defined in the CCP driver. The CCP driver
>>>> provides snp_guest_ext_guest_request() that is used by the KVM to get
>>>> both the report and certificate data at once.
>>>>
>>>> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
>>>> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
>>>> Signed-off-by: Michael Roth <michael.roth@....com>
>>>> ---
>>>>   arch/x86/kvm/svm/sev.c | 185 
>>>> +++++++++++++++++++++++++++++++++++++++--
>>>>   arch/x86/kvm/svm/svm.h |   2 +
>>>>   2 files changed, 181 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
>>>> index 5f2b2092cdae..18efa70553c2 100644
>>>> --- a/arch/x86/kvm/svm/sev.c
>>>> +++ b/arch/x86/kvm/svm/sev.c
>>>> @@ -331,6 +331,7 @@ static int sev_guest_init(struct kvm *kvm, 
>>>> struct kvm_sev_cmd *argp)
>>>>           if (ret)
>>>>               goto e_free;
>>>> +        mutex_init(&sev->guest_req_lock);
>>>>           ret = sev_snp_init(&argp->error, false);
>>>>       } else {
>>>>           ret = sev_platform_init(&argp->error);
>>>> @@ -2051,23 +2052,34 @@ int sev_vm_move_enc_context_from(struct kvm 
>>>> *kvm, unsigned int source_fd)
>>>>    */
>>>>   static void *snp_context_create(struct kvm *kvm, struct 
>>>> kvm_sev_cmd *argp)
>>>>   {
>>>> +    struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
>>>>       struct sev_data_snp_addr data = {};
>>>> -    void *context;
>>>> +    void *context, *certs_data;
>>>>       int rc;
>>>> +    /* Allocate memory used for the certs data in SNP guest request */
>>>> +    certs_data = kzalloc(SEV_FW_BLOB_MAX_SIZE, GFP_KERNEL_ACCOUNT);
>>>> +    if (!certs_data)
>>>> +        return NULL;
>>>> +
>>>>       /* Allocate memory for context page */
>>>>       context = snp_alloc_firmware_page(GFP_KERNEL_ACCOUNT);
>>>>       if (!context)
>>>> -        return NULL;
>>>> +        goto e_free;
>>>>       data.gctx_paddr = __psp_pa(context);
>>>>       rc = __sev_issue_cmd(argp->sev_fd, SEV_CMD_SNP_GCTX_CREATE, 
>>>> &data, &argp->error);
>>>> -    if (rc) {
>>>> -        snp_free_firmware_page(context);
>>>> -        return NULL;
>>>> -    }
>>>> +    if (rc)
>>>> +        goto e_free;
>>>> +
>>>> +    sev->snp_certs_data = certs_data;
>>>>       return context;
>>>> +
>>>> +e_free:
>>>> +    snp_free_firmware_page(context);
>>>> +    kfree(certs_data);
>>>> +    return NULL;
>>>>   }
>>>>   static int snp_bind_asid(struct kvm *kvm, int *error)
>>>> @@ -2653,6 +2665,8 @@ static int snp_decommission_context(struct kvm 
>>>> *kvm)
>>>>       snp_free_firmware_page(sev->snp_context);
>>>>       sev->snp_context = NULL;
>>>> +    kfree(sev->snp_certs_data);
>>>> +
>>>>       return 0;
>>>>   }
>>>> @@ -3174,6 +3188,8 @@ static int sev_es_validate_vmgexit(struct 
>>>> vcpu_svm *svm, u64 *exit_code)
>>>>       case SVM_VMGEXIT_UNSUPPORTED_EVENT:
>>>>       case SVM_VMGEXIT_HV_FEATURES:
>>>>       case SVM_VMGEXIT_PSC:
>>>> +    case SVM_VMGEXIT_GUEST_REQUEST:
>>>> +    case SVM_VMGEXIT_EXT_GUEST_REQUEST:
>>>>           break;
>>>>       default:
>>>>           reason = GHCB_ERR_INVALID_EVENT;
>>>> @@ -3396,6 +3412,149 @@ static int snp_complete_psc(struct kvm_vcpu 
>>>> *vcpu)
>>>>       return 1;
>>>>   }
>>>> +static unsigned long snp_setup_guest_buf(struct vcpu_svm *svm,
>>>> +                     struct sev_data_snp_guest_request *data,
>>>> +                     gpa_t req_gpa, gpa_t resp_gpa)
>>>> +{
>>>> +    struct kvm_vcpu *vcpu = &svm->vcpu;
>>>> +    struct kvm *kvm = vcpu->kvm;
>>>> +    kvm_pfn_t req_pfn, resp_pfn;
>>>> +    struct kvm_sev_info *sev;
>>>> +
>>>> +    sev = &to_kvm_svm(kvm)->sev_info;
>>>> +
>>>> +    if (!IS_ALIGNED(req_gpa, PAGE_SIZE) || !IS_ALIGNED(resp_gpa, 
>>>> PAGE_SIZE))
>>>> +        return SEV_RET_INVALID_PARAM;
>>>> +
>>>> +    req_pfn = gfn_to_pfn(kvm, gpa_to_gfn(req_gpa));
>>>> +    if (is_error_noslot_pfn(req_pfn))
>>>> +        return SEV_RET_INVALID_ADDRESS;
>>>> +
>>>> +    resp_pfn = gfn_to_pfn(kvm, gpa_to_gfn(resp_gpa));
>>>> +    if (is_error_noslot_pfn(resp_pfn))
>>>> +        return SEV_RET_INVALID_ADDRESS;
>>>> +
>>>> +    if (rmp_make_private(resp_pfn, 0, PG_LEVEL_4K, 0, true))
>>>> +        return SEV_RET_INVALID_ADDRESS;
>>>> +
>>>> +    data->gctx_paddr = __psp_pa(sev->snp_context);
>>>> +    data->req_paddr = __sme_set(req_pfn << PAGE_SHIFT);
>>>> +    data->res_paddr = __sme_set(resp_pfn << PAGE_SHIFT);
>>>> +
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +static void snp_cleanup_guest_buf(struct sev_data_snp_guest_request 
>>>> *data, unsigned long *rc)
>>>> +{
>>>> +    u64 pfn = __sme_clr(data->res_paddr) >> PAGE_SHIFT;
>>>> +    int ret;
>>>> +
>>>> +    ret = snp_page_reclaim(pfn);
>>>> +    if (ret)
>>>> +        *rc = SEV_RET_INVALID_ADDRESS;
>>>> +
>>>> +    ret = rmp_make_shared(pfn, PG_LEVEL_4K);
>>>> +    if (ret)
>>>> +        *rc = SEV_RET_INVALID_ADDRESS;
>>>> +}
>>>> +
>>>> +static void snp_handle_guest_request(struct vcpu_svm *svm, gpa_t 
>>>> req_gpa, gpa_t resp_gpa)
>>>> +{
>>>> +    struct sev_data_snp_guest_request data = {0};
>>>> +    struct kvm_vcpu *vcpu = &svm->vcpu;
>>>> +    struct kvm *kvm = vcpu->kvm;
>>>> +    struct kvm_sev_info *sev;
>>>> +    unsigned long rc;
>>>> +    int err;
>>>> +
>>>> +    if (!sev_snp_guest(vcpu->kvm)) {
>>>> +        rc = SEV_RET_INVALID_GUEST;
>>>> +        goto e_fail;
>>>> +    }
>>>> +
>>>> +    sev = &to_kvm_svm(kvm)->sev_info;
>>>> +
>>>> +    mutex_lock(&sev->guest_req_lock);
>>>> +
>>>> +    rc = snp_setup_guest_buf(svm, &data, req_gpa, resp_gpa);
>>>> +    if (rc)
>>>> +        goto unlock;
>>>> +
>>>> +    rc = sev_issue_cmd(kvm, SEV_CMD_SNP_GUEST_REQUEST, &data, &err);
>>>
>>>
>>> This one goes via sev_issue_cmd_external_user() and uses sev-fd...
>>>
>>>> +    if (rc)
>>>> +        /* use the firmware error code */
>>>> +        rc = err;
>>>> +
>>>> +    snp_cleanup_guest_buf(&data, &rc);
>>>> +
>>>> +unlock:
>>>> +    mutex_unlock(&sev->guest_req_lock);
>>>> +
>>>> +e_fail:
>>>> +    svm_set_ghcb_sw_exit_info_2(vcpu, rc);
>>>> +}
>>>> +
>>>> +static void snp_handle_ext_guest_request(struct vcpu_svm *svm, 
>>>> gpa_t req_gpa, gpa_t resp_gpa)
>>>> +{
>>>> +    struct sev_data_snp_guest_request req = {0};
>>>> +    struct kvm_vcpu *vcpu = &svm->vcpu;
>>>> +    struct kvm *kvm = vcpu->kvm;
>>>> +    unsigned long data_npages;
>>>> +    struct kvm_sev_info *sev;
>>>> +    unsigned long rc, err;
>>>> +    u64 data_gpa;
>>>> +
>>>> +    if (!sev_snp_guest(vcpu->kvm)) {
>>>> +        rc = SEV_RET_INVALID_GUEST;
>>>> +        goto e_fail;
>>>> +    }
>>>> +
>>>> +    sev = &to_kvm_svm(kvm)->sev_info;
>>>> +
>>>> +    data_gpa = vcpu->arch.regs[VCPU_REGS_RAX];
>>>> +    data_npages = vcpu->arch.regs[VCPU_REGS_RBX];
>>>> +
>>>> +    if (!IS_ALIGNED(data_gpa, PAGE_SIZE)) {
>>>> +        rc = SEV_RET_INVALID_ADDRESS;
>>>> +        goto e_fail;
>>>> +    }
>>>> +
>>>> +    mutex_lock(&sev->guest_req_lock);
>>>> +
>>>> +    rc = snp_setup_guest_buf(svm, &req, req_gpa, resp_gpa);
>>>> +    if (rc)
>>>> +        goto unlock;
>>>> +
>>>> +    rc = snp_guest_ext_guest_request(&req, (unsigned 
>>>> long)sev->snp_certs_data,
>>>> +                     &data_npages, &err);
>>>
>>> but this one does not and jump straight to 
>>> drivers/crypto/ccp/sev-dev.c ignoring sev->fd. Why different? Can 
>>> these two be unified? sev_issue_cmd_external_user() only checks if fd 
>>> is /dev/sev which is hardly useful.
>>>
>>> "[PATCH RFC v7 32/64] crypto: ccp: Provide APIs to query extended 
>>> attestation report" added this one.
>>
>> SNP_EXT_GUEST_REQUEST additionally returns a certificate blob and 
>> that's why it goes through the CCP driver interface 
>> snp_guest_ext_guest_request() that is used to get both the report and 
>> certificate data/blob at the same time.
> 
> True. I thought though that this calls for extending sev_issue_cmd() to 
> take care of these extra parameters rather than just skipping the sev->fd.
> 
> 
>> All the FW API calls on the KVM side go through sev_issue_cmd() and 
>> sev_issue_cmd_external_user() interfaces and that i believe uses 
>> sev->fd more of as a sanity check.
> 
> Does not look like it:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/crypto/ccp/sev-dev.c?h=v6.2-rc3#n1290 
> 
> 
> ===
> int sev_issue_cmd_external_user(struct file *filep, unsigned int cmd,
>                  void *data, int *error)
> {
>      if (!filep || filep->f_op != &sev_fops)
>          return -EBADF;
> 
>      return sev_do_cmd(cmd, data, error);
> }
> EXPORT_SYMBOL_GPL(sev_issue_cmd_external_user);
> ===
> 
> The only "more" is that it requires sev->fd to be a valid open fd, what 
> is the value in that? I may easily miss the bigger picture here. Thanks,
> 
> 

Have a look at following functions in drivers/crypto/ccp/sev-dev.c:
sev_dev_init() and sev_misc_init().

static int sev_misc_init(struct sev_device *sev)
{
         struct device *dev = sev->dev;
         int ret;

         /*
          * SEV feature support can be detected on multiple devices but
          * the SEV FW commands must be issued on the master. During
          * probe, we do not know the master hence we create /dev/sev on
          * the first device probe.
          * sev_do_cmd() finds the right master device to which to issue
          * the command to the firmware.
	 */
...
...

Hence, sev_issue_cmd_external_user() needs to ensure that the correct 
device (master device) is being operated upon and that's why there is 
the check for file operations matching sev_fops as below :

int sev_issue_cmd_external_user(struct file *filep, unsigned int cmd,
                                 void *data, int *error)
{
         if (!filep || filep->f_op != &sev_fops)
                 return -EBADF;
..
..

Essentially, sev->fd is the misc. device created for the master PSP 
device on which the SEV/SNP firmware commands are issued, hence,
sev_issue_cmd() uses sev->fd.

Thanks,
Ashish	

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